Database Schema Designer — From Requirements to DDL

Design a database schema for [application/feature description].

**Requirements:**
[describe what the system needs to store and the key operations]

**Deliverables:**

1. **Entity-Relationship summary**: List entities, their relationships (1:1, 1:N, M:N), and cardinality
2. **Table definitions** (DDL):
   - Column names, types, constraints (NOT NULL, UNIQUE, CHECK)
   - Primary keys (prefer UUID/CUID over sequential for distributed systems)
   - Foreign keys with ON DELETE behavior
   - Timestamps: created_at, updated_at on every table
3. **Indexes**:
   - Primary lookup patterns → indexes
   - Composite indexes for common WHERE + ORDER BY combos
   - Partial indexes where applicable
4. **Normalization check**: Confirm 3NF, justify any intentional denormalization
5. **Sample queries**: Top 5 most common queries with their expected EXPLAIN cost
6. **Migration script**: Full CREATE TABLE statements, ready to run

**Database**: [PostgreSQL / MySQL / SQLite]
**Scale expectations**: [rows per table in 1 year]
**Multi-tenancy**: [single-tenant / multi-tenant with tenant_id / separate schemas]